1format(n) Tcl Built-In Commands format(n)
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8 format - Format a string in the style of sprintf
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11 format formatString ?arg arg ...?
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16 This command generates a formatted string in a fashion similar to the
17 ANSI C sprintf procedure. FormatString indicates how to format the
18 result, using % conversion specifiers as in sprintf, and the additional
19 arguments, if any, provide values to be substituted into the result.
20 The return value from format is the formatted string.
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23 The command operates by scanning formatString from left to right. Each
24 character from the format string is appended to the result string
25 unless it is a percent sign. If the character is a % then it is not
26 copied to the result string. Instead, the characters following the %
27 character are treated as a conversion specifier. The conversion speci‐
28 fier controls the conversion of the next successive arg to a particular
29 format and the result is appended to the result string in place of the
30 conversion specifier. If there are multiple conversion specifiers in
31 the format string, then each one controls the conversion of one addi‐
32 tional arg. The format command must be given enough args to meet the
33 needs of all of the conversion specifiers in formatString.
34 Each conversion specifier may contain up to six different parts: an
36 XPG3 position specifier, a set of flags, a minimum field width, a pre‐
37 cision, a size modifier, and a conversion character. Any of these
38 fields may be omitted except for the conversion character. The fields
39 that are present must appear in the order given above. The paragraphs
40 below discuss each of these fields in turn.
41 If the % is followed by a decimal number and a $, as in “%2$d”, then
43 the value to convert is not taken from the next sequential argument.
44 Instead, it is taken from the argument indicated by the number, where 1
45 corresponds to the first arg. If the conversion specifier requires
46 multiple arguments because of * characters in the specifier then suc‐
47 cessive arguments are used, starting with the argument given by the
48 number. This follows the XPG3 conventions for positional specifiers.
49 If there are any positional specifiers in formatString then all of the
50 specifiers must be positional.
51 The second portion of a conversion specifier may contain any of the
53 following flag characters, in any order:
54 - Specifies that the converted argument should be left-justi‐
56 fied in its field (numbers are normally right-justified with
57 leading spaces if needed).
58 + Specifies that a number should always be printed with a sign,
60 even if positive.
61 space Specifies that a space should be added to the beginning of
63 the number if the first character is not a sign.
64 0 Specifies that the number should be padded on the left with
66 zeroes instead of spaces.
67 # Requests an alternate output form. For o and O conversions it
69 guarantees that the first digit is always 0. For x or X con‐
70 versions, 0x or 0X (respectively) will be added to the begin‐
71 ning of the result unless it is zero. For all floating-point
72 conversions (e, E, f, g, and G) it guarantees that the result
73 always has a decimal point. For g and G conversions it spec‐
74 ifies that trailing zeroes should not be removed.
75 The third portion of a conversion specifier is a decimal number giving
77 a minimum field width for this conversion. It is typically used to
78 make columns line up in tabular printouts. If the converted argument
79 contains fewer characters than the minimum field width then it will be
80 padded so that it is as wide as the minimum field width. Padding nor‐
81 mally occurs by adding extra spaces on the left of the converted argu‐
82 ment, but the 0 and - flags may be used to specify padding with zeroes
83 on the left or with spaces on the right, respectively. If the minimum
84 field width is specified as * rather than a number, then the next argu‐
85 ment to the format command determines the minimum field width; it must
86 be an integer value.
87 The fourth portion of a conversion specifier is a precision, which con‐
89 sists of a period followed by a number. The number is used in differ‐
90 ent ways for different conversions. For e, E, and f conversions it
91 specifies the number of digits to appear to the right of the decimal
92 point. For g and G conversions it specifies the total number of digits
93 to appear, including those on both sides of the decimal point (however,
94 trailing zeroes after the decimal point will still be omitted unless
95 the # flag has been specified). For integer conversions, it specifies
96 a minimum number of digits to print (leading zeroes will be added if
97 necessary). For s conversions it specifies the maximum number of char‐
98 acters to be printed; if the string is longer than this then the trail‐
99 ing characters will be dropped. If the precision is specified with *
100 rather than a number then the next argument to the format command
101 determines the precision; it must be a numeric string.
102 The fifth part of a conversion specifier is a size modifier, which must
104 be ll, h, or l. If it is ll it specifies that an integer value is
105 taken without truncation for conversion to a formatted substring. If
106 it is h it specifies that an integer value is truncated to a 16-bit
107 range before converting. This option is rarely useful. If it is l it
108 specifies that the integer value is truncated to the same range as that
109 produced by the wide() function of the expr command (at least a 64-bit
110 range). If neither h nor l are present, the integer value is truncated
111 to the same range as that produced by the int() function of the expr
112 command (at least a 32-bit range, but determined by the value of
113 tcl_platform(wordSize)).
114 The last thing in a conversion specifier is an alphabetic character
116 that determines what kind of conversion to perform. The following con‐
117 version characters are currently supported:
118 d Convert integer to signed decimal string.
120 u Convert integer to unsigned decimal string.
122 i Convert integer to signed decimal string (equivalent to d).
124 o Convert integer to unsigned octal string.
126 x or X Convert integer to unsigned hexadecimal string, using digits
128 “0123456789abcdef” for x and “0123456789ABCDEF” for X).
129 c Convert integer to the Unicode character it represents.
131 s No conversion; just insert string.
133 f Convert number to signed decimal string of the form xx.yyy,
135 where the number of y's is determined by the precision
136 (default: 6). If the precision is 0 then no decimal point is
137 output.
138 e or E Convert number to scientific notation in the form x.yyye±zz,
140 where the number of y's is determined by the precision
141 (default: 6). If the precision is 0 then no decimal point is
142 output. If the E form is used then E is printed instead of
143 e.
144 g or G If the exponent is less than -4 or greater than or equal to
146 the precision, then convert number as for %e or %E. Other‐
147 wise convert as for %f. Trailing zeroes and a trailing deci‐
148 mal point are omitted.
149 % No conversion: just insert %.
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153 The behavior of the format command is the same as the ANSI C sprintf
154 procedure except for the following differences:
155 [1] %p and %n specifiers are not supported.
157 [2] For %c conversions the argument must be an integer value, which
159 will then be converted to the corresponding character value.
160 [3] The size modifiers are ignored when formatting floating-point
162 values. The ll modifier has no sprintf counterpart.
163
165 Convert the numeric value of a UNICODE character to the character
166 itself:
167 set value 120
168 set char [format %c $value]
169 Convert the output of time into seconds to an accuracy of hundredths of
171 a second:
172 set us [lindex [time $someTclCode] 0]
173 puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]
174 Create a packed X11 literal color specification:
176 # Each color-component should be in range (0..255)
177 set color [format "#%02x%02x%02x" $r $g $b]
178 Use XPG3 format codes to allow reordering of fields (a technique that
180 is often used in localized message catalogs; see msgcat) without
181 reordering the data values passed to format:
182 set fmt1 "Today, %d shares in %s were bought at $%.2f each"
183 puts [format $fmt1 123 "Global BigCorp" 19.37]
184 set fmt2 "Bought %2\$s equity ($%3$.2f x %1\$d) today"
186 puts [format $fmt2 123 "Global BigCorp" 19.37]
187 Print a small table of powers of three:
189 # Set up the column widths
190 set w1 5
191 set w2 10
192 # Make a nice header (with separator) for the table first
194 set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
195 puts $sep
196 puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
197 puts $sep
198 # Print the contents of the table
200 set p 1
201 for {set i 0} {$i<=20} {incr i} {
202 puts [format "| %*d | %*ld |" $w1 $i $w2 $p]
203 set p [expr {wide($p) * 3}]
204 }
205 # Finish off by printing the separator again
207 puts $sep
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210 scan(n), sprintf(3), string(n)
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213 conversion specifier, format, sprintf, string, substitution
214Tcl 8.1 format(n)